JP2014179206A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve preserving characteristics under, for instance, a high-temperature environment by efficiently capturing HF generated from a fluorine system solvent being oxidatively decomposed at a positive electrode surface.SOLUTION: A nonaqueous electrolyte secondary battery 10 includes: a positive electrode 20 in which a positive electrode active material layer 22 is formed on a positive electrode collector 21; a negative electrode 30; a separator 40; and a nonaqueous electrolyte containing fluorine based solvent. A silica is contained between the positive electrode active material layer 22 and the separator 40 or in the positive electrode active material layer 22.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a lithium ion secondary battery.

Methods have been proposed for capturing hydrofluoric acid (HF) generated by the reaction between water and an electrolyte salt in a non-aqueous solvent to improve storage characteristics (thermal stability) (for example, Patent Documents 1 and 2). reference). Specifically, Patent Document 1 discloses a separator for a non-aqueous electrolyte secondary battery that is made of glass having an organic polymer and silica (SiO ₂ ) as a main component, and includes 50 wt% to 90 wt% of glass. Yes. Patent Document 2 discloses a lithium polymer secondary battery in which a polyvinylidene fluoride-based thin film layer in which silica is dispersed is disposed to face a negative electrode.

JP 2005-11614 A JP 2002-33128 A Special table 2007-504628

  By the way, in order to further improve the storage characteristics under a high temperature environment, it has been proposed to use fluoroethylene carbonate as a non-aqueous solvent (see, for example, Patent Document 3). When a fluorinated solvent is included as the non-aqueous solvent, the fluorinated solvent oxidizes and decomposes on the positive electrode surface to generate HF. The generation of such HF is remarkable when a fluorinated cyclic carbonate such as fluoroethylene carbonate is used as the fluorinated solvent, and is particularly remarkable when the positive electrode potential exceeds 4.50 V on the basis of metallic lithium. HF generated on the surface of the positive electrode dissolves Co and Ni constituting the positive electrode active material, which causes deterioration in storage characteristics.

  Note that the technologies disclosed in Patent Documents 1 and 2 do not assume the capture of HF generated by oxidative decomposition of the fluorine-based solvent on the surface of the positive electrode, and cannot capture such HF efficiently.

  A nonaqueous electrolyte secondary battery according to the present invention includes a nonaqueous electrolyte comprising a positive electrode in which a positive electrode active material layer is formed on a positive electrode current collector, a negative electrode, a separator, and a nonaqueous electrolyte containing a fluorine-based solvent. An electrolyte secondary battery comprising silica between a positive electrode active material layer and a separator or in a positive electrode active material layer.

  According to the nonaqueous electrolyte secondary battery of the present invention, HF generated by the oxidative decomposition of the fluorine-based solvent on the surface of the positive electrode can be efficiently captured, and for example, storage characteristics in a high temperature environment can be improved.

It is sectional drawing of the electrode body which comprises the nonaqueous electrolyte secondary battery which is an example of embodiment of this invention. It is sectional drawing which shows the modification of an electrode body.

Hereinafter, embodiments according to the present invention will be described in detail.
As shown in FIG. 1, a nonaqueous electrolyte secondary battery 10 which is an example of an embodiment of the present invention includes a nonaqueous electrolyte (not shown) including a positive electrode 20, a negative electrode 30, a separator 40, and a fluorine-based solvent. With. The structure of the electrode body of the nonaqueous electrolyte secondary battery 10 is not particularly limited, and may be a wound type in which the positive electrode 20 and the negative electrode 30 are wound through the separator 40, or the positive electrode 20 and the negative electrode 30. May be a laminated type in which the separators 40 are alternately laminated. The exterior body that accommodates the electrode body and the non-aqueous electrolyte is not particularly limited, and may be a metal case or a laminate packaging material.

  Further, the non-aqueous electrolyte secondary battery 10 is characterized by containing silica between the positive electrode active material layer 22 of the positive electrode 20 and the separator 40 or in the positive electrode active material layer 22. As will be described in detail later, silica plays a role of capturing HF generated on the surface of the positive electrode 20.

[Positive electrode 20]
The positive electrode 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22 formed on the current collector. The positive electrode active material layer 22 is preferably formed on both surfaces of the positive electrode current collector 21. The thickness of the positive electrode current collector 21 is, for example, 10 μm to 40 μm. The thickness of the positive electrode active material layer 22 is, for example, 20 μm to 100 μm. The volume average particle diameter (Dv ₅₀ ) of the positive electrode active material contained in the positive electrode active material layer 22 is, for example, ₅ μm to 20 μm.

  As the positive electrode current collector 21, a conductive thin film sheet, particularly a metal foil or alloy foil that is stable in the potential range of the positive electrode 20, a film having a metal surface layer, or the like can be used. The metal constituting the positive electrode current collector 21 is preferably a metal containing aluminum as a main component, for example, aluminum or an aluminum alloy.

The positive electrode active material layer 22 preferably contains a conductive material and a binder in addition to the positive electrode active material. Examples of the positive electrode active material include lithium-containing transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Examples of the lithium-containing transition metal oxide include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _{1 -y} O ₂ , Li _x Co _y M _{1 -y} O _z , and Li _x Ni _{1. -y M y O z, Li x} Mn 2 O 4, Li x Mn 2-y M y O 4, LiMPO 4, Li 2 MPO 4 F (M; Na, Mg, Sc, Y, Mn, Fe, Co, At least one of Ni, Cu, Zn, Al, Cr, Pb, Sb, and B). Here, 0 <x ≦ 1.2 (value immediately after the production of the active material, which increases or decreases due to charge / discharge), 0 <y ≦ 0.9, and 2.0 ≦ z ≦ 2.3.

  The conductive agent is used to increase the electrical conductivity of the positive electrode active material layer. Examples of the conductive agent include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more. The binder is used to maintain a good contact state between the positive electrode active material and the conductive agent and to enhance the binding property of the positive electrode active material and the like to the surface of the positive electrode current collector. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or a modified product thereof is used. The binder may be used in combination with a thickener such as carboxymethyl cellulose (CMC) or polyethylene oxide (PEO).

End-of-charge potential of the positive electrode 20, from the viewpoint of high capacity, preferably 4.25V (vs.Li/Li ⁺⁾ or more, 4.40V (vs.Li/Li ⁺⁾ or more preferred. The upper limit of the charge termination potential of the positive electrode is not particularly limited, but is preferably 4.8 V (vs. Li ^/ Li ⁺ ) or less from the viewpoint of suppressing decomposition of the nonaqueous electrolyte.

[Negative electrode 30]
The negative electrode 30 includes a negative electrode current collector 31 and a negative electrode active material layer 32 formed on the current collector. The negative electrode active material layer 32 is preferably formed on both surfaces of the negative electrode current collector 31. The thickness of the negative electrode current collector 31 is, for example, about 5 μm to 20 μm. The thickness of the negative electrode active material layer 32 is, for example, 20 μm to 100 μm.

  As the negative electrode current collector 31, a conductive thin film sheet, particularly a metal foil or alloy foil that is stable in the potential range of the negative electrode 30, a film having a metal surface layer, or the like can be used. The metal constituting the negative electrode current collector 31 is preferably a metal mainly composed of copper.

  For example, the negative electrode active material layer 32 preferably contains a binder in addition to the negative electrode active material capable of inserting and extracting lithium ions. Examples of the negative electrode active material include natural graphite, artificial graphite, lithium, silicon, carbon, tin, germanium, aluminum, lead, indium, gallium, lithium titanate, and alloys and mixtures thereof. As the binder, PTFE or the like can be used as in the case of the positive electrode, but styrene-butadiene copolymer (SBR) or a modified body thereof is preferably used. The binder may be used in combination with a thickener such as CMC.

[Separator 40]
As the separator 40, a porous sheet having ion permeability and insulating properties is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. As a material for the separator 40, cellulose, or an olefin resin such as polyethylene or polypropylene is preferable. The thickness of the separator 40 is, for example, 10 μm to 40 μm. The separator 40 has, for example, a porosity of 30% to 70% and an average pore diameter of 10 nm to 500 nm.

[Non-aqueous electrolyte]
The non-aqueous electrolyte includes a non-aqueous solvent containing a fluorinated solvent and an electrolyte salt dissolved in the non-aqueous solvent. The nonaqueous electrolyte is not limited to a liquid electrolyte (nonaqueous electrolyte solution), and may be a solid electrolyte using a gel polymer or the like. As the fluorine-based solvent, at least a fluorinated cyclic carbonate is used, and a fluorinated chain ester is preferably used in combination. Alternatively, a non-fluorinated solvent may be used in combination.

  As the fluorinated cyclic carbonate, it is preferable to use fluoroethylene carbonate or a derivative thereof. Examples of the fluoroethylene carbonate include 4-fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, and 4,4,5-trifluoroethylene carbonate. Of these, 4-fluoroethylene carbonate (hereinafter referred to as “FEC”) is particularly preferable from the viewpoint of storage characteristics and the like.

  The content of the fluorinated cyclic carbonate such as FEC is preferably 5% by volume to 30% by volume with respect to the total volume of the nonaqueous solvent in the nonaqueous electrolyte from the viewpoint of storage characteristics and the like. When the content of the fluorinated cyclic carbonate is less than 5% by volume, good storage characteristics may not be obtained. On the other hand, if it exceeds 30% by volume, a large amount of gas may be generated in the electrolytic solution, which is disadvantageous in terms of cost.

  The fluorinated chain ester is preferably at least one selected from a fluorinated chain carbonate ester and a fluorinated chain carboxylate ester. As the fluorinated chain carbonate, a lower chain carbonate such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl isopropyl carbonate is partially or entirely replaced with fluorine. That is suitable. Examples of the fluorinated chain carboxylic acid ester include lower chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, or ethyl propionate in which part or all of hydrogen is substituted with fluorine. Is preferred.

  It is also possible to use a non-fluorinated solvent in combination with the non-aqueous solvent. Non-fluorinated solvents include cyclic carbonates such as ethylene carbonate (EC), lactams such as 2-methyl-1-pyrrolidone, cyclic carbamates such as 3-methyl-2-oxazolidinone, and cyclic sulfones such as tetramethylene sulfone. Chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate, chain carboxylic acids such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl isobutyrate, and methyl trimethyl acetate Esters, ketones such as pinacholine, 1,2-dimethoxyethane, tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,3-dioxane, ethers such as 1,4-dioxane, N, N-dimethylformamide, , N- chain amides of dimethylacetamide, N, N- dimethylcarbamoyl-methyl, N, etc. N- dimethylcarbamoyl chain carbamic acid esters such as methyl and the like. Of these, it is particularly desirable to use a chain ester carbonate.

The electrolyte salt is preferably a lithium salt. As the lithium salt, those generally used as a supporting salt in a conventional nonaqueous electrolyte secondary battery can be used. Specific examples include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , CH ₃ SO ₃ Li, LiCF ₃ SO ₃ , LiCl, LiBr, LiB (C ₆ H ₅ ) ₄ , LiC (CF _{3 SO 2) 3, LiB (C} 2 O 4) 2 and the like. These lithium salts may be used alone or in combination of two or more.

[Silica layer 50]
The nonaqueous electrolyte secondary battery 10 contains silica between the positive electrode active material layer 22 and the separator 40 or in the positive electrode active material layer 22 as described above. For example, the silica is preferably formed in a layer shape on the surface of the positive electrode active material layer 22 or the surface of the separator 40 facing the positive electrode 20. In the example shown in FIG. 1, a silica layer 50 is interposed between the positive electrode active material layer 22 and the separator 40.

The silica particles constituting the silica layer 50 are mainly composed of SiO ₂ (for example, 99% or more) and may contain some metal elements other than Si (Na, Fe, Ni, Cr, etc.). . SiO ₂ reacts with HF as follows. Thereby, HF generated on the surface of the positive electrode 20 due to the oxidative decomposition of the fluorinated solvent, particularly the fluorinated cyclic carbonate, can be efficiently captured, and deterioration of the positive electrode active material can be suppressed.
4HF + SiO ₂ → SiF ₄ + 2H ₂ O
SiF ₄ + 2HF → H ₂ SiF ₆

  The silica layer 50 may be provided, for example, on the surface of the positive electrode active material layer 22 or may be provided on the surface of the separator 40 facing the positive electrode 20, but the latter is preferable from the viewpoint of ease of application. . Moreover, although the silica layer 50 may be provided in both the positive electrode active material layer 22 and the separator 40, it is preferable to provide in one (especially separator 40) from viewpoints of productivity. In any case, in this embodiment, the silica layer 50 is disposed between the surface of the separator 40 facing the positive electrode 20 and the surface of the positive electrode active material layer 22 (hereinafter, the silica layer 50 is It is assumed that it is formed on the surface of the separator 40). The silica layer 50 is preferably formed over the entire area of the surface of the separator 40 facing the positive electrode 20.

  The silica layer 50 may be composed only of silica, but is preferably composed of silica particles and a binder resin. The binder resin adheres silica particles to the surface of the separator 40 and also bonds the silica particles together. The binder resin is not particularly limited as long as it is a resin that exhibits the adhesive force. For example, a hydrophilic polymer such as polycarboxylic acid or polyvinyl alcohol can be used. The silica layer 50 can be formed by dispersing silica particles in water in which a binder resin is dissolved or dispersed, applying the silica particles on the separator 40, and drying.

The Dv ₅₀ of the silica particles is preferably larger than the average pore diameter of the separator 40 and sufficiently smaller than the Dv _{50 of} the positive electrode active material. Specifically, 1/10 or less of Dv ₅₀ of the positive electrode active material is preferable, and 1/20 or less is more preferable. The Dv ₅₀ of the silica particles is preferably, for example, ₅₀ nm to ₅₀₀ nm, more preferably 100 nm to 500 nm, and particularly preferably 200 nm to 400 nm. If dv ₅₀ is within the range, without clogging the separator 40, thereby improving the reactivity with HF. The Dv ₅₀ of the silica particles can be measured by a laser diffraction / scattering particle size distribution measuring device or observation with an electron microscope.

  The content of the silica particles is preferably determined according to HF generated by oxidative decomposition of the fluorine-based solvent. In the present embodiment, the thickness of the silica layer 50 is appropriately changed according to the content of the silica particles. The suitable thickness of the silica layer 50 varies somewhat depending on the content of silica particles, but is generally 1 μm to 5 μm. The content of silica particles in the silica layer 50 (with respect to the total weight of the layer) is, for example, 90% by weight to 99.5% by weight.

  When FEC is used as the fluorinated solvent, the content of silica particles in the entire battery is 1/6 mol (16.7 mol% with respect to FEC) with respect to 1 mol of FEC. Thereby, HF can be captured over a long period of time. FEC decomposes gradually, particularly at higher potentials, but by including silica particles in this proportion, all HF can be theoretically captured even when all FECs are oxidatively decomposed. In addition, since the fluorinated chain ester is less oxidatively decomposed than the fluorinated cyclic carbonate, when the both are used in combination, it is preferable to determine the content of the silica particles based on the latter content. .

  The content of the silica particles is preferably 5 mol% to 25 mol%, more preferably 5 mol% to 17 mol% (16.7 mol%) with respect to FEC from the viewpoint of storage characteristics, capacity density, and the like. In the case of a battery used in a general environment, the content of silica particles is preferably 5 mol% as a lower limit and 17 mol% as an upper limit with respect to FEC. Thereby, it is possible to efficiently achieve both high-temperature storage characteristics and capacity density.

  As described above, the nonaqueous electrolyte secondary battery 10 includes the silica layer 50 including silica particles between the positive electrode 20 and the separator 40. The silica layer 50 efficiently captures HF generated on the surface of the positive electrode by the silica particles contained in the layer without inhibiting the movement of lithium ions. Thereby, deterioration of the positive electrode active material is suppressed, and good high-temperature storage characteristics and cycle characteristics can be obtained. The configuration of the nonaqueous electrolyte secondary battery 10 is particularly suitable when a fluorinated cyclic carbonate is used as the nonaqueous solvent.

The design of the above embodiment can be changed as appropriate without departing from the object of the present invention.
For example, the porous silica layer 50 may be formed by applying an alcohol solution of silicate such as tetraethoxysilane (TEOS) or silica sol onto the separator 40. In this case, the silica layer can be formed without using a binder resin.

  In addition, as shown in FIG. 2, the positive electrode active material layer 22 may include a silica particle 60. The positive electrode active material layer 22 illustrated in FIG. 2 includes positive electrode active material particles 23, a binder 24, a conductive material 25, and silica particles 60. Also in this case, it is preferable to determine the content of the silica particles 60 based on the content of the fluorinated solvent. The positive electrode slurry to which the silica particles 60 are added can be coated on the positive electrode current collector 21 to disperse the silica particles 60 in the positive electrode active material layer 22.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to these Examples.

<Example 1>
[Production of positive electrode]
Li ₁ Ni _0.5 Co _0.2 Mn _0.3 O ₂ as a positive electrode active material, carbon as a conductive material, and PVdF as a binder were mixed at a weight ratio of 95: 2.5: 2.5. Thereafter, it was added to an N-methyl-2-pyrrolidone (NMP) solution and kneaded to prepare a positive electrode slurry. The slurry was applied to both surfaces of an aluminum foil as a positive electrode current collector so as to have a predetermined coating amount, dried, and then rolled to a predetermined packing density to produce a positive electrode.

(Production of negative electrode)
Graphite, which is a negative electrode active material, styrene butadiene (SBR) rubber, which is a binder, and CMC, which is a thickener, are mixed in a weight ratio of 98: 1: 1 and then kneaded in an aqueous solution. Thus, a negative electrode slurry was prepared. The negative electrode slurry was applied on both sides of a copper foil as a negative electrode current collector so as to have a predetermined coating amount, dried, and then rolled to a predetermined packing density to produce a negative electrode.

[Preparation of non-aqueous electrolyte]
As a nonaqueous solvent, 0.5 mL of a mixed solvent in which FEC and fluoroethyl methyl carbonate (FEMC) were mixed at a volume ratio of 25:75 was used. LiPF ₆ as a lithium salt was dissolved in the mixed solvent so as to be 1 mol / L to prepare a nonaqueous electrolytic solution.

(Formation of silica layer)
As the separator, a polyethylene porous sheet (thickness: 30 μm) was used. Then, a silica layer was formed on one surface of the separator. The silica layer was formed by applying an aqueous silica dispersion on a separator with a gravure coater and drying. The silica water dispersion is composed of silica particles having a volume average particle diameter of 200 nm (manufactured by M-Tech Chemical Co., Optisilica SR-200P), polyacrylic acid (Wako Pure Chemical Industries, 168-07375) as a binder resin, water, Were mixed at a weight ratio of 9: 89.7: 1.3. The thickness of the silica layer was adjusted to about 2 μm so that the content of silica particles was 10 μg (about 20 mol% with respect to FEC).

[Production of battery]
The positive electrode and the negative electrode were arranged so as to face each other with the separator interposed therebetween, to prepare an electrode body. At this time, as described above, the surface of the separator on which the silica layer is formed is arranged facing the positive electrode side. Subsequently, the electrode body was inserted into an exterior body made of a laminate material formed by laminating polyethylene terephthalate, aluminum or the like. At this time, each electrode tab protrudes from the end of the exterior body.

Next, in a glove box under an inert gas atmosphere, the nonaqueous electrolyte solution was injected so as to impregnate the electrode body in the outer package, and then the opening was heat sealed. The ratio of the positive electrode capacity and the negative electrode capacity was adjusted so that the end-of-charge voltage was 4.6 V (positive electrode potential 4.7 V (vs. Li ^/ Li ⁺ )) and the capacity was 50 mAh. Test cell A1 which is a secondary battery was produced.

<Example 2>
Test cell A2 was produced in the same manner as in Example 1 except that the content of silica with respect to FEC was changed to 5 mol%.

<Example 3>
Test cell A3 was produced in the same manner as in Example 1 except that the content of silica with respect to FEC was 25 mol%.

<Example 4>
Test cell A4 was produced in the same manner as in Example 1 except that the content of silica relative to FEC was 3 mol%.

<Example 5>
Test cell A5 was produced in the same manner as in Example 1 except that the content of silica relative to FEC was 1 mol%.

<Comparative Example 1>
Test cell X1 was produced in the same manner as in Example 1 except that the silica layer was not formed.

<Comparative example 2>
Test cell X2 was produced in the same manner as in Example 2 except that the formation position of the silica layer was changed from the surface facing the positive electrode of the separator to the surface facing the negative electrode.

[Evaluation of charge storage characteristics at a battery voltage of 4.6 V (metal lithium reference: 4.7 V)]
The charge storage characteristics were evaluated for each of the test cells A1 to A4, X1, and X2.
First, at 25 ° C., the battery voltage is charged to 4.6 V with a constant current (0.5 C) −constant voltage (0.02 C cut), and discharged to 2.5 V with a constant current (0.5 C). by, the discharge capacity was measured D ₁ of the before storage. Next, after charging to a battery voltage of 4.6 V with a constant current (0.5 C) -constant voltage (0.02 C cut), each battery was stored in a thermostat at 80 ° C. for 5 days. The battery after the storage test was discharged at a constant current (0.5 C) to a battery voltage of 2.5 V to determine the remaining capacity D ₂ after storage.

The capacity remaining rate (%) after storage is calculated by the following formula from the discharge capacity D ₁ before storage and the remaining capacity D ₂ after storage. A higher capacity remaining rate means better charge storage characteristics. The evaluation results are shown in Table 1.
Capacity remaining rate after storage (%) = (D ₂ / D ₁ ) × 100

  As shown in Table 1, in each of the test cells A1 to A5 of the example, the high-temperature storage characteristics are improved as compared with the test cell X1 of Comparative Example 1 that does not contain silica. In particular, increasing the amount of silica relative to FEC improves the high-temperature storage characteristics. In addition, the content of silica is preferably 5 mol% to 25 mol% based on the amount of FEC. Considering the capacity density, 5 mol% is particularly preferable.

  Also, when a silica layer was formed on the surface facing the negative electrode of the separator (Comparative Example 2), 1% improvement in storage characteristics was confirmed, but when a silica layer was formed on the surface facing the positive electrode (implementation) The degree of improvement is small compared to Example 2). That is, by interposing silica between the positive electrode and the separator, it is possible to efficiently improve the high temperature storage characteristics.

  DESCRIPTION OF SYMBOLS 10 Nonaqueous electrolyte secondary battery, 20 positive electrode, 21 positive electrode current collector, 22 positive electrode active material layer, 30 negative electrode, 31 negative electrode current collector, 32 negative electrode active material layer, 40 separator, 50 silica layer

Claims (7)

A nonaqueous electrolyte secondary battery comprising a positive electrode in which a positive electrode active material layer is formed on a positive electrode current collector, a negative electrode, a separator, and a nonaqueous electrolyte containing a fluorine-based solvent,
A nonaqueous electrolyte secondary battery containing silica between the positive electrode active material layer and the separator or in the positive electrode active material layer. The nonaqueous electrolyte secondary battery according to claim 1,
The fluorine-based solvent is a non-aqueous electrolyte secondary battery containing at least 4-fluoroethylene carbonate. The nonaqueous electrolyte secondary battery according to claim 2,
The non-aqueous electrolyte secondary battery in which the silica is contained at a ratio of at least 1/6 mol with respect to 1 mol of the 4-fluoroethylene carbonate. The nonaqueous electrolyte secondary battery according to claim 2,
The non-aqueous electrolyte secondary battery in which the silica is contained at a ratio of 5 mol% to 25 mol% with respect to the 4-fluoroethylene carbonate. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4,
The non-aqueous electrolyte secondary battery in which the silica is formed into a layer on the surface of the positive electrode active material layer or the surface of the separator. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5,
The silica is a non-aqueous electrolyte secondary battery having a volume average particle diameter of 50 nm to 500 nm. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6,
A nonaqueous electrolyte secondary battery in which the potential of the positive electrode at full charge is 4.25 V or more based on metallic lithium.

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